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Multiplicative age-season adjustment factors for milk and fat yields of five breeds of dairy goats were estimated by fitting a three-way, mixed classification model containing random effects for does with fixed effects for herd-year-season and age-season for 7544, 1994, 7456, 3307, and 4599 lactation records collected from 1965 to 1976 from Alpine, La- Mancha, Nubian, Saanen, and Toggenburg dairy goats in the United States. These factors reflect changes in milk and fat yields associated with age and season of freshening. As with dairy cattle, these factors indicated that milk records of goats are affected differently in different seasons for a particular age. Season of freshening affected younger does more than their older herdmates. Does freshening in January through March produced larger milk yields than their herdmates that freshened at later months of the year. In general, does reached peak production at 34 to 38 mo of age and declined after 50 mo of age.
Repeatabilities for milk yield were . 33, .29, .35, .27, and .35 for Alpine, La- Mancha, Nubian, Saanen, and Toggenburg breeds. The adjustment factors indicate that age factors for dairy cows currently being used for adjusting goat records should be replaced by separate factors developed for specific breeds of dairy goats. No such set of age-season adjustment factors has been adopted universally for dairy goats in the United States. Factors in this study, however, could serve as a guide for such a set of adjustment factors.